This invention relates to a magnetic bubble memory apparatus and more particularly a sheild structure thereof for preventing external noise.
As shown by a block diagram in FIG. 1, a prior art magnetic bubble memory apparatus is constituted by an interface controller 1 including a bubble memory controller, a timing controller 2, pulse current drive circuits 3, source of power supply 4, signal detector 5 and a magnetic bubble memory device 6 and is connected to a central processing unit 7.
Usually, since the signal taken out from the bubble memory device are very small, for example of the order of several mV, it is necessary to amplify such a small output to a level of several hundred mV and then detect the signal. The detected signal is then sent to a processing unit. During such amplification of several hundreds times, the signal is greatly affected by ambient noise. Accordingly, the magnetic bubble memory device 6 and the signal detector 5 should be used at a place remote from a source of noise.
Specifically, the signal detector 5 has a circuit construction as exemplified in FIG. 2. This circuit is connected to receive a bubble detection output signal of several millivolts from a pair of magnetoresistive detectors. The detection signal is superimposed on a noise generated under the application of a rotating magnetic field. The noise is cancelled by a differential preamplifier IC1 and only the bubble output is taken out. The gain of the preamplifier IC1 is set to about 100 times to amplify the bubble output signal from several millivolts to several of hundreds of millivolts. The thus amplified bubble output signal is fed to a dual sense amplifier IC2, and the presence or absence of the bubble output signal is detected at the timing of a strobe pulse STR-P (from timing controller 2) and converted into a TTL level signal. This signal is then fed to a dual D-type positive edge-triggered flip-flop IC3 and a data latched at the timing of the strobe signal is applied to the interface controller 1. Such a signal detector as described above is very susceptible to ambient noise.
With increased use of the magnetic memory device in recent years, it became necessary to develop a portable magnetic bubble memory apparatus of cassette type capable of being readily exchanged with a recorded memory device. Such a magnetic bubble apparatus is constructed such that the magnetic bubble memory device and the susceptive signal detector are contained in a cassette.
Since the cassette of the magnetic bubble memory apparatus has a small size and is easy to handle, it is often located near a CRT or a keyboard of TTY and it is liable to be influenced by noise created thereby.